1. Field of the Invention
The present invention relates to a brake system so called "brake by wire system" in which the state of a braking operation by a driver is converted to an electric signal for inducing a wheel braking force.
2. Description of Related Art
The brake by wire system is well known. In this system, an electric signal representing the state of brake pedal operation by a driver, i.e., the amount of brake pedal stroke or brake pedal depression pressure, is generated. A wheel braking force can be induced based on the electric signal. The conventional brake by wire system employs, as examples for inducing a wheel braking force, a method of directly pressing a brake pad against a brake disk separately in each wheel by using ultrasonic motors or a method of producing a wheel cylinder pressure by using a two-position valve and a pump, as disclosed in Japanese patent Laid-open publication No. Hei 9-188242, under the title of "brake fluid pressure control apparatus".